Variable resistor constructions



April 14, 1959 M. E. BoURNs ET A1. 2,882,375

VARIABLE REsIsToR coNsTRucToNs Filed July 26. 1954 United States Patent O 2,882,375 VARIABLE RESISTUR 'CONSTRUCTIONS Marlan E. Bourns, Wilbur T. Hardison, and Warren D. Hulbert, Riverside, Calif.; said Hardison and said Hulbert assiguors to Bourns Laboratories, Inc.

Application July 26, 1954, Serial No.445,534 7 Claims. (Cl. 201-62) The present invention is concerned with new and improved variable resistor constructions. More specilically it is concerned with extremely small resistors, although, obviously many of the constructional details herein described ar-e capable yof being used on comparatively large electrical components of the class described. A broad object of the invention is to provide new and improved variable resistor constructions. A more speciic object is to provide variable resistors which are comparatively cheap to construct, reliable in operation, and which can be manufactured in very small size. Further areas or objects of this invention will be apparent from the remainder of this specification.

This invention may be summarized as being concerned with variable resistors each having an elongated housing, preferably formed of an insulating material within which there is disposed at least one resistance member, another electrically conductive member which may be a resistance member, a metallic contact member, and means for moving this contact member with respect to the resistance member and the electrically conductive member, and

with an external resistance film 16. Both the member 14 'and the cylinder 15 are held in position between the sections 11 by means of insulating ledges 17 extending along the sides 18 of the sections 11 between the ends 19 of these sections. Electrical connections to the member 14 and the cylinder 15 are made by means of conductive terminals 20 which are each formed so as to have a shank section 21 projecting through the ends 19 of the sections 11. The terminals 20 include upstanding center portions 22 positioned so as to lie against the internal surfaces of the ends 19 and bent over contact sections 23- which are designed to engage either the member 14 or the extremities of the cylinder 15 with a spring action so as to at all times be in electrical contact with this member 14 and the lilm 16.

A threaded metallic shaft 24 extending beyond the sections 11 is held within semi-cylindrical depressions 25 in the ends 19 of the sections 11 so as to project generally parallel to the ledges 17, the member 14 and the cylinder 15. Adjacent to the exterior of these sections 11 the shaft 24 is provided with slots 26 which are engaged by insulating caps 27 of a resin such as indicated above or like material formed so as to encase the portions of shaft 24 projecting from the ends 19. These caps 27 are each provided with slots 28 designed to be engaged j with a screw driver so that the shaft 24 can be turned.

from which housing there project appropriate electrical terminal members and said means for moving the meftallic contact member. The invention is more fully summarized by the appended claims. Further details of the invention are best apparent from the balance `of this specification, the appended claims, and the accompanying drawings, in which:

c Figure l is a top view of a resistor of the invention;

Figure 2 is a partial cross-sectional view taken at line 2-2 of Figure 1;

Figure 3 is a cross-sectional view taken at line 3-3 of Figure 2;

Figure 4 is a view similar to Figure 2 of a modied .construction of the invention;

Figure 5 is a cross-sectional view taken at line 5-5 of Figure`4;

: Figure 6 is a View simil-ar to Figure 2 of a second modiied construction of the invention;

Figure 7 is a cross-sectional view taken at line 7-7 of Figure 6;

Figure 8 is an isometric view of a resistance member which may be employed with the invention', and

Figure 9 is a view similar to Figure 3 of a third modified construction of the invention.

The various items shown in the drawings have been drawn so as to best illustrate particular features as will be more fully described. For this reason the majority of parts shown in the various figures are not necessarily to the scaleof proposed commercial units embodying the constructions shown.

In Figures 1, 2, and 3 of the drawings there is `shown a variable resistor construction 10 which includes bilaterally symmetrical shell-like sections 11 formed of yan insulating material such as a lled phenolic resin, which sections are secured together by rivets 12 so as to form a complete housing within which there is disposed a conductive metallic member 14 and a cylinder 15 provided A contact member 30 formed of a single strip of metal bent so as to have a first side 31, a second side 32 attached to said first side 31 by a iirst `apex 33 and man-V ufactured so -as to have aligned apertures 34 and 35 within the sides 32 and 31 respectively, is placed between the sections 11 with the shaft projecting through the apertures 34 and 35. The exact shape of these apertures may be varied within wide limits. Preferably however, they are of generally oval shape so that as the sides 31 and 32 `are pressed toward one another the shaft 24 may be easily inserted through them and so that as these sides are released the openings will be brought into engagement with the shaft 24 because of the inherent resiliency of the material from which the contact mem-- ber 30 is formed. Preferably at least one of the apertures 34 or 35 is formed so as to have edges which are designed in a conventional manner to engage the threads upon the shaft 24 so that as the shaft is turned the contact member 30 is moved upon it. The portions of the shaft 24 immediately adjacent to the sections 11 are preferably not threaded so that -as the contact member 30 approaches the end of its travel toward the right, the right-hand end of the side 31 releases the threads of the leadscrew 24 and then runs up against the end 19 of the housing. This causes the right-hand side 31 to stop, while the left-hand side 32 continues to be driven toward the right by the `leadscrew thread. As the sides 31, 32 are squeezed together in this manner, the aperture 34 in the left-hand side 32 is tilted up more nearly perpendicular to the axis of the leadscrew, until the thread of the leadscrew finally becomes disengaged from the edge of the aperture, and thereafter slips or ratchets over the edge of 4the aperture. This releasing action prevents the contact member from being forcibly jammed against the end wall 19 by the leadscrew and thereby damaged. When rotation of the leadscrew is reversed, the spring pressure of the compressed contact member 30 causes the latter to reengage the threads of the leadscrew and move toward the left. The releasing action is the same `at the left-hand end of the instrument, except that in this case the foot 36 engages the terminal clip 23 to stop the travel of the the second side 32 by means of a second apex 37. This apex 37 is designed to ride against the surface of the member resistance filmv 16 as the shaft 24 is turned. During such motion the parts of the contact member 30 adjacent to the ledges 17 holding the member 14 in position engage these edges, preventing rotation of the member 30. The contact member 30 also includes an attached member 38 projecting from either of said sides 31 or 32 beyond said first apex 33. This member 38 includes an upturned end 39 attached to it by means of a third apex 40. This third apex 40 is designed to engage the member 14 so as to at all times be in electrical contact with it. It is considered obvious from the drawings that the entire contact member 30 may be conveniently manufactured eration and that the apexes 37 and 40 are designed to be held against the member 14 and the film 16 as indicated with a spring-like action resulting from the inherent resiliency of the material from which the contact member 30 is manufactured.

The assembly of the variable resistor construction is essentially exceedingly simple, and marks one of the major advantages of this specic construction. In manufacturing it one of the sections 11 is placed upon a Vtable or other supporting surface and the various parts specifically indicated in the preceding discussion are merely laid in position upon it. The terminals are inserted into slots 42 formed in the section 11 so as to be biased against the conductive member with which they make contact before the other of the sections 11 is applied to the unit. Similarly the contact member 30 is placed in substantially its final position, and then as the other section 11 is positioned over the section 11 upon the supporting surface and all of the various parts are trapped in assembled relation. The construction 10 is completed by heading over the rivets 12 in an obvious manner. If desired, other equivalent fastening means such as an adhesive can be employed instead of these rivets.

The modified construction 50 shown in Figures 4 and 5 is composed of two shell-like sections 51 and 52 comwhichare designed to fit with a resistance composition 54 which may, if desired, be molded in situ, or may,

if desired, be inserted within against the exterior surface 57 center portions 58 designed to formed within the section 51, at

of the section 51, attached fit within notches 59 terminals 65 including exterior portions 66 which are intended to fit against the exterior surface of the section 51. These terminals 65 also include center portions 68 which are designed to fit within notches 69 formed within the sections 52 and attached internal portions 62 lying against the surface of the internal cavity 63. The terminals 65 each contain an end section 70 bent into the general shape of the cylinder 64. As is illustrated in Figure 5 these sections 70 are designed to engage the cylinder 64 with a spring-like action forming electrical contact with the resistance coating 67. If desired, the

f manner as the shaft 24. This shaft exerted by the ends 70 may be provided with terminal extremities 71 which are designed to engage -a surface of the cavity 63 remote from the surface of this cavity engaged by the internal portions 62 so as to firmly hold the terminals 65 in position within the section 52 by a spring-like action.

Within the construction 50 there is provided a metallic contact member of substantially the same construction as the contact member 30 shown in Figures 2 and 3 of the drawing. Because of the similarity of constructional details between the two contact members like parts of each are designated by the same numerals. The contact member 75 is carried by an elongated shaft 76 formed of an insulating material so as to be threaded in the same 76 is designed to project from both ends of the construction 50 through depressions 77 of substantially semi-circular configuration formed in the sections 51 and 52, and is designed to be held in place by collars 78 formed on the shaft 76 bearing against the surfaces of the cavities 53 and 63. With this specific. construction the member 76 may be turned causing the appropriate parts on the contact member 75 to engage the resistance coating 67 and the resistance come position 54 in the expected manner. When the final con-l struction 50 is assembled the sections 51 and 52 are preferably secured together by an appropriate adhesive although other equivalent means may be used.

In Figures 6 and 7 of the drawing a second modified construction 80 of the invention comprising a shelllike section 81 of an insulating material defining together with a lid 82 of a transparent insulating material such as Lucite, Plexiglas, etc., a complete housing having an internal cavity 83 is shown. The lid 82 and the section 81 are normally secured together by an adhesive or other. equivalent means. Within the section 81 there is provided a resistance composition 84 which may, like the composition 54, be either positioned within the supporting section 81 or be molded in situ within this section. Terminal connections are made to the composition 84 by means of electrically conductive rivets 85 which are either molded within the section 81 or are inserted within apertures in this section after it has been formed. Each of the rivets 85 is secured in the obvious manner to small metal terminal tabs 86 positioned upon the outside section 81.

Located within an aperture 87 formed within an end of the section 81 so as to project from this end 88 into a circular depressed cavity 106 formed within the other end 88 of the section 81 is a conductive shaft 90 which is threaded intermediate its ends and preferably has an Unthreaded end portion engaging the cavity 106, this Unthreaded portion having a cross-sectional diameter equal to or slightly smaller than the minor diameter of the threaded portion of the shaft 90, such that the contact member 105 may disengage the threaded portion of the shaft upon reaching the right-hand travel extremity, there by preventing the breakage of the housing by turning the shaft 90 an excessive number of revolutions. The contact member 105 is so constructed that spring pressure end of the contact member 105 against the inside of the internal cavity 83 causes the spring to again engage the threaded portion of the shaft 90 when the shaft 90 is turned in a reverse direction, causing the contact spring to move toward the left-hand end of the instrument. This shaft is secured in position by means of a tab 107 formed integrally with the lid 82 projecting from this lid so as to engage a groove 108 formed within the shaft 90. This shaft is also secured to a non-conductive cap 92 externally of the section 81 by means of non-conductive pins 91; this cap 92 is provided with a `slot 93 of the conventional type designed to receive a screw driver. Electrical contact is made to the shaft 90 by means of a metal terminal 95 including a portion 96r adapted to lie along the outside of the section 81, a center section 97 designed to fit within a notch 98 within this section 81 and a portion 99 designed to fit against the internal surface of the.,

essere l 'section 81 in sucha manner that the entire terminal 95 is held inv position with a spring or clip-like action. The portion 99 of the terminal 9S is provided with an end section 100 which is normally biased by a spring-action, resulting from the inherent resiliency of the material from which the terminal 95 is manufactured, against a cylindrical section 101 of the shaft 90 so as to be in electrical contact with this shaft as it is turned.

The shaft 90 carries a contact member 105 of substantially the same construction as the contact member 30 except for the omission of the attached member 38 projecting `from the contact member 30. Because of the similarity of construction details the same numbers are used to designate parts of the contact member 105 as are used to designate equivalent parts of the contact member 30.

One important feature of the specific construction shown in Figures 6 and 7 of the drawings relates to the fact that the positionl of the contact member 105 within the construction 80 is readily visible through the lid 82. If desired, various markings may be applied to this lid 82,

which correspond to the position of the apex 33 of the contact member 105 or to other parts ofthe contact member so that at all times it is possible to accurately determine the position of the contact member within the construction 80.

In Figure 9 of the drawings there is shown a variable resistor construction 110 which diiers from construction 80 shown in Figures 6 and 7 in only several minor regards. This specific construction 110 involves the use of a non-conductive lid 111 to which there is secured either by means of an adhesive or by metallizing techniques a thin layer of a conductive metal 112, This lid is used to cover a shell-like sectiton 113 formed of an insulating material so as to define an internal cavity 114 and is secured to this shell-like section by means of an adhesive or like means in such a manner that the layer 112 faces this internal cavity 114. This cavity is of such dimension as to easily hold a shaft 116 which carries a contact member (not shown). Both the shaft and the contact member employed with this embodiment of the invention are substantially identical to the equivalent members employed in the construction 80 illustrated in Figures 6 and 7.

The contact member employed in the embodiment of Figure 9 is adapted to move against a wound resistance unit of a type specifically illustrated in Figure 8 of the drawings as including a generally oval cross-sectioned elongated body 118 of an insulating material around which there are positioned a number of turns 119 of a resistance wire. These turns 119 are of the conventional category employed in wire-wound resistors and are connected at one end of the body 118 to a large mass or group of turns 120 of the same resistance wire. The unit 115 is designed so that the contact member employed is intended to make contact with the turns 119. With this construction the turns 120 provide a large resistance value icoupled with what in effect amounts to a very tine adjustfrnent of the resistance by the use of the turns 119.

The resistance unit 115 employed in the construction 110 is normally held in position by means of spring clips 121 having opposed bowed sides 122 positioned against -opposed sides of the cavity 114 in such a manner that these sides engage the resistance unit 115 when this unit is inserted within the cavity 114 so as to hold it irmly in place. The spring clips used are disposed at opposite Iends of the cavity 114 in such a manner that they make contact with the portions of the windings or turns 119 `and 120 farthest removed from one another. Both of these spring clips 121 are provided with bottom walls 123 connected to the sides 122. These bottom walls 123 are so designed as to pass together outwardly through an appropriate aperture (not shown) within the section 113 in a conventional manner.

With the construction 110 electrical contact is made to the layer 112 by means of a terminal 125 which is imbedded within the walls of the section 11,3 as indicated in Flgure 9 of the drawing so as to project from both the bottom of this section adjacent to the spring clips 121 and so as to project from the walls of the section 113 into` the internal cavity 114 adjacent to the top of this cavity. There the terminal 125 is provided with an end 126 which is adapted to be held against the layer 112 by spring tension so as to be in electrical contact with this layer.

The various variable resistor constructions illustrated in the accompanying drawings and described in the aforegoing discusison constitute a very distinct advance in the art in that they are all extremely reliable in operation and yet are extremely simple to easily and cheaply produce on a production line basis. Further, many of the operative parts of the resistor constructions described, such as, for example, the contact members indicated, may be easily and cheaply fabricated and are exceedingly reliable for use with other constructions besides those specifically indicated. Inasmuch as all of the resistors shown employ housings which are non-conductive, these resistors are immune from shorting troubles which have plagued other related resistor constructions. The resistors herein described are specically intended to be manufactured having a cross-section size of approximately s by 1A inch.

Those skilled in the art will realize that a number of minor modiications may be made within the precise constructional details indicated without departing from the scope of this invetnion. All such modifications of this category which are within the skill of the art are to be considered as part of this invention.

We claim:

l. A variable resistor comprising a housing having a cavity formed therein, a resistance element mounted on said housing within said cavity, a rotatable leadscrew disposed generally parallel to said resistance element, a contact member having a releasable driving connection with the thread of said leadscrew whereby the contact member is moved along the length of said resistance element by rotation of the leadscrew, said contact member wiping on said resistance element, and stationary means engageable by said contact member as the latter approaches the end of its travel for releasing said driving connection, whereby said contact member is prevented from being forcibly jammed against the end of said hous ing and thereby damaged.

2. A variable resistor comprising a split shell housing made up of two cooperating sections that are joined together to form an enclosed hollow body, the adjoining faces of said housing sections being provided with opposed formations that coact to form axially aligned bear ings, a leadscrew journaled at its ends in said bearings, a resistance element disposed within said housing, opposed formations in said housing sections which engage said resistance element to locate and secure the same, and a contact member movable by said leadscrew and wiping on said resistance element.

3. A variable resistor comprising a split shell housing made up of two substantially symmetrical sections that are joined together to form an enclosed hollow body, the adjoining faces of said housing sections being provided with opposed semicyclindrical cavities that coact to form axially aligned cylindrical bearings, a leadscrew having axially spaced portions journaled in said bearings, a resistance element disposed within said housing, ledges projecting inwardly from opposite sides of said sections parallel to said resistance element, said ledges engaging the sides of said resistance element to locate and secure the same with respect to the housing, and a contact member having threaded engagement with said leadscrew and wiping on said resistance element.

4. A variable resistor comprising a split shell housing made up of two cooperating sections that are joined together to form an enclosed hollow body, the adjoining faces of said housing sections being provided with opposed formations thatv coact to form axially aligned bear-v ings, a, leadscrew journeled at its, ends in said bearings, al resistance element disposed within said housing, atleast one termina-tion tab extending housing and having an inner edge contacting said. resistance element to malte electrical contact therewith, and al contact member movable. by said leadscrew andV wiping on saidy resistance element.

5. A variable. resistor comprising a split shell housing made up of twocooperating sections that are joined.A t0.-V get-her to. forni an enclosed hollowbody, the adjoining faces of said housing sections being provided with op-` nosed ormations that enact to form axially aligned bearings, a leadscrew journaled at its endsy in said bearings, a resistance element disposed within said housing, a pair of termination tabs of resilient spring metal extending through Openings in the wall: of said housingand having their inner ends. bent to contact opposite ends of said resistance element with spring pressure, and a contact member having threaded engagement with said l'eadscrew and wiping-on said resistance. element.

6. A variable resistor comprising a split shell housing made up of two cooperating sections that are joined together to form an enclosed hollow body, the adjoining faces of said housing sections being provided with opposed formations that coact to form axially aligned bearings, a leadscrew journaled at its ends in said' bearings, a resistance element disposed within said housing, a pair of termination tabs, of resilient spring metal extending through the walls of said housing and having their inner ends bent to overlie and contact opposite ends of said resista-nce element with spring pressure, a contact member having a driving connection with the. thread of said leadscrew and wiping on said resistance elementz through the wall 0f said as said Contact.. member se as. to prevent said' contact nielnbertreinv being fjerei.-

bly. jammed against. the end-ef. said hensing and damaged.

' thereby- 7,.. In a variable resister havingl a housingy a. leadserew retetebly supported within said housing. and a resistance. element mounted. on, said, housing generally parallel, t0 said leadscrew, the improvement comprising a contact member of resilient sheet rnetall bent to form two angularly related sides, saidV sides, having aligned apertures formed therein1 which are, of such size that said lead'screw can. be passed freely through them. when said sides are squeezed together, said apertures engaging said leadscrew,

on opposite sides thereof when said contact member sides. are released,y and atleast one. edge of said apertures having an operating engagement with the thread of said leadserew, one ofsaid. contact. I nenlber sides being ex.-

tended; and having a. portion wiping 0n. said resistance element- References Cited theI tile of this patent UNITED STATES PATENTS.

with the'thread of said leadscrewv eppremhes the end efits travel. 

